The Park Grass Experiment

There's a lot to learn from it

A few weeks ago, on the ct_turf podcast, Dr. Micah Woods and I discussed whether a turf system fertilized with only ammonium sulfate would/could remain free of Poa annua. It turns out, just such an experiment exists, and it’s been going on for 166 years. The Park Grass experiment in Rothamsted, England is the oldest ecological experiment in existence. Personally, I find this study fascinating.   

In 2011, Dr. Woods and Dr. Frank Rossi wrote an article for the April 22 issue of the USGA Green Section Record. The article, titled The Park Grass Experiment and the Fight Against Dogma does a better job than I ever could of explaining the experiment. I highly recommend you read it. If you’ve read it before, you should read it again–I just did!

The TLDR summary is this:

• Grasses tend to dominate when nitrogen is the only fertilizer applied.

• The addition of lime and other nutrients encourages the growth of weeds.

• Study plots only ever fertilized with ammonium sulfate are dominated by colonial bentgrass (Agrostis capillaris) and sweet vernal grass (Anthoxanthum odoratum), but no broadleaf weeds.

The Park Grass study makes two things clear to me:

1. Fertilizing with only ammonium sulfate will impact the species populating your turf.

2. Effects from fertilizing in this way do not come immediately; it takes some amount of time. 

From Woods and Rossi’s article:

Other studies on the manipulation of pH for reducing annual bluegrass populations or reducing earthworm populations show little to no benefit in the first three years of a study, but after eight to ten years and longer demonstrate the value of a long-term commitment to a practice. Most courses that have low pH have little annual bluegrass and low earthworm populations.